The present invention relates to a method of drying brown coal and, more particularly, to a method of drying brown coal which can obviate various problems in handling and transportation of dried brown coal.
Nowadays, most of energy consumed in the civilized society owes to petroleum. In the 1960's, an additional petroleum deposite of 5 billion Kl as a mean has been confirmed every year. This petroleum deposite additionally confirmed is said to amount to 35 years' supply of petroleum, when calculated on the basis of present rate of yield per year. However, from now on, the new exploitation of the petroleum will be concentrated to areas where the natural conditions are extremely severe. These severe conditions will render the discovery of new petroleum deposits increasingly difficult with regard to both the aspect of exploitation technique and fund.
Even if an additional discovery of petroleum deposite of 5 billion Kl per year is possible in the future, the amount of petroleum reserves will be reduced to 20 years' supply 13 years after now and to 5 years' supply 28 years after now. It is clear that the world will face a limit to the exploitation of petroleum technically and financially, within several decades. Thus, it will become extremely difficult to obtain petroleum in an amount necessary for meeting the energy demand, particularly for those countries having little oil resources under their grounds.
Under these circumstances, there is an increasing demand for new energy techniques as measures for avoiding future energy crisis.
One of these measures is to exploit and use brown coal as a new energy source. The utilization of the brown coal has not been yet developed in spite of its low price and abundance. It is estimated that there is a deposite of wood coal and brown coal of 2 trillion tons over the world. In fact, a deposite of 2700 billion tons of wood coal and brown coal, which amounts to 1350 billion tins in coal base, has been confirmed, 39%, 34% and 18% of which belong to U.S. Sr, European countries and Australia.
The brown coal burried under the territory of, for example, Australia contains 66.7 to 50% of water, 0.7 to 4.9% of ash content, 16.8 to 24.8% of volatile matter and 15.8% to 23.5% of fixed carbon.
One of the most serious defects of the brown coal is the large water content. The transportation cost will be raised unless the water content is suitably removed. It is therefore essential to dry and dehydrate the brown coal when the brown coal is used for industrial purposes.
In most cases, the natural brown coal exists in the form of extremely fine particles of a particle size of about 40.mu. or smaller, bonded to one another. Therefore, when the natural brown coal is dried and dehydrated, these fine particles are freed from one another to take the form of powders, incurring various problems such as environmental pollution by the scattering of fine particles, difficulty in handling and so forth. In addition, the bulk density of the brown coal in the dried state is as low as about 0.3, which considerably raises the cost of transportation. Further, there is a danger of spontaneous combustion of the powders of brown coal during transportation and storage.